1. Field of the Invention
The present invention is directed to an insulated electrical conducting assembly which includes an electrical conductor and an insulating annular laminate surrounding the conductor which meets the requirements imposed on electrical conducting assemblies utilized in the engine compartments of road vehicles.
2. Background of the Prior Art
Insulation of electrical conducting assemblies, of which the most common example is cables, employed in road vehicles must meet several requirements to ensure proper performance of the vehicle engine during operating conditions. These requirements include all those imposed upon electrical cables generally as well as those particularly critical to road vehicle engine performance. Among the requirements of electrical conducting assembly insulation that are particularly critical to vehicle engine performance are heat aging, flame resistance and abrasion resistance.
The first of these requirements, heat aging, requires the insulation of road vehicle cables to be resistant to thermal oxidation. Specifically, the polymer or polymers included in the insulation composition must be resistant to the degradative effects of extended exposure to the elevated temperature environment of a road vehicle engine compartment. Those skilled in the art are aware that extended exposure of polymeric resins to high temperature leads to thermal oxidation which degrades the polymer. This is commonly referred to as xe2x80x9cheat aging.xe2x80x9d
Thus, a particularly important test to which road vehicle cables are subjected is heat aging resistance. In this test, two test cable samples are subjected to elevated temperature over long periods of time. For example, road vehicle cables are subjected to the so-called short term aging test, set forth in ISO International Standard 6722, Paragraph 10.1. In this test a test cable is subjected to a temperature equal to the sum of the class rating temperature and 25xc2x0 C. for a period of 240 hours. The class rating temperature varies from 85xc2x0 C. to 250xc2x0 C. depending upon the location where the cable is disposed. Thus, the test temperature ranges from 110xc2x0 C.xc2x12xc2x0 C. to 275xc2x0 C.xc2x14xc2x0 C. At the end of this period the cable assembly is subjected to a winding test in a freezing chamber during which time the cable visually inspected to insure that the insulation is undisturbed. Thereafter, the electrical effectiveness of the cable is tested.
Alternatively, the cable is subjected to a long term aging test. This test is set forth in ISO 6722, Paragraph 10.2. In this test two cable samples are subjected to the temperature equivalent to the class rating for 3,000 hours. The test temperature thus varies between 85xc2x0 C.xc2x12xc2x0 C. and 250xc2x0 C.xc2x14xc2x0 C. depending upon the location of the cable in the vehicle. Thereupon, the cable is subjected to a winding test at room temperature and then judged as in the short term aging test.
Heat aging, a problem successfully addressed in the United States, which has more stringent requirements than those imposed in foreign countries since engines of U.S. manufactured vehicles are, on average, larger and enclosed in smaller engine compartments, is a growing problem in countries where, until recently, engines were smaller and enclosed in larger compartments. In these countries, heat aging is a growing concern in the design of automobile and other road vehicle cable insulation.
A second major concern in the design of road vehicle cable insulation is abrasion resistance. The insulation currently in use in cables employed in foreign built vehicles meet abrasion resistance testing standards. However, these insulators do not meet the stringent heat aging requirements of newly designed vehicles. Therefore, the insulation of cables designed for use in future vehicles are currently being redesigned to meet higher heat aging requirements. These new insulators will be required to still meet stringent abrasion resistance testing. Specifically, cables used in foreign built vehicles must meet the Scrape Abrasion Resistance Test of International Standard ISO 6722, as set forth in Paragraph 9.2. That test, like the heat aging testing, discussed above, of ISO 6722 is incorporated herein by reference.
Flame resistance or more precisely, resistance to flame propagation, a requirement common to cables used in other applications, is a critical property requirement of electrical conductive assemblies employed in road vehicles. Indeed, the aforementioned ISO 6722 International Standard concerning road vehicle cables includes, in Paragraph 12, a flame propagation resistance test.
The above remarks establish the need in the art for a new electrical conducting assembly insulator which, in addition to meeting all the other requirements imposed on an electrical conducting assembly insulator, possesses the requisite heat aging characteristics and meets stringent abrasion resistant tests increasingly imposed on cables utilized in road vehicles.
A particularly pertinent prior art reference which discloses insulators for electrical conduits employed in road vehicles is U.S. Pat. No. 5,412,012. That patent describes a flame retardant insulation and jacketing composition useful for wire and cable products which exhibits improved adhesion to the metal conductor. That insulating composition includes a crosslinked ethylene copolymer which may be an ethylene-vinyl ester copolymer, an ethylene-alkyl acrylate copolymer, an ethylene-alkyl methacrylate copolymer or mixtures thereof. The composition further includes a hydrated inorganic filler, an alkoxysilane and stabilizers to protect against the deleterious effects of heat, air and light.
Another pertinent reference is U.S. Pat. No. 5,439,965 which describes a flame retardant and abrasion resistant crosslinkable composition useful as wire and cable insulation. The composition includes an ethylene-vinyl acetate copolymer having a vinyl acetate content of 5 to 12 wt. %, a halogenated flame retardant additive, antimony trioxide as a synergist and an organic peroxide.
Many prior art references illustrate the utilization of electrical conductors covered by multilayer insulators wherein at least one of the layers imparts flame resistivity to the insulator. U.S. Pat. No. 5,670,748 is illustrative of a teaching of such an insulating laminate. The ""748 patent sets forth a flame retardant and smoke suppressant electrical conducting assembly insulator which comprises an electrical conductor surrounded by an inner layer of a polyolefin or polyurethane foam and an outer layer of a halogenated polymeric material, surrounding the inner layer, which renders the insulating laminate flame retardant and smoke suppressant.
U.S. Pat. No. 5,410,106 illustrates another electrical conducting assembly employing a multilayer insulator. The assembly of the ""106 patent is utilized in an electrical feed cable in which a plurality of electrical conductors are insulated with an inner layer of an ethylene-xcex1-olefin copolymer surrounded by a protective outer layer of a fiberglass, carbon fiber or composite tape inorganic fiber cloth.
A similar design is disclosed in U.S. Pat No. 3,571,490. The ""490 patent sets forth a flame resistant electrical cable which includes a plurality of insulated conductors, each conductor including a metal strand surrounded by a vulcanized copolymer or terpolymer of ethylene and propylene which acts as a flame resistant electrical insulator. The insulator, an ethylene-propylene polymer, i.e. EPM or EPDM, is covered with a layer of neoprene or chlorosulfonated polyethylene.
U.S. Pat. No. 5,378,856 describes a transmission cable insulator employed in the distribution of electrical power in commercial and residential buildings. The insulator includes non-halogenated polyethylene, which in a preferred embodiment is high density polyethylene; non-halogenated ethylene-vinyl acetate; a flame retardant; a processing aid; a flame retardant enhancer, such as a silicone fluid; a lubricant and flame retardant enhancer, such as magnesium stearate; and an antioxidant, such as hindered phenolics. The insulator, in contact with the electrical conductor, in one embodiment includes a cable jacket wrapped about the insulator. The cable jacket, not laminated to the insulator, is not identified in the patent.
A new electrical conducting assembly has now been developed which, in addition to meeting all other requirements imposed upon electrical conduits used in road vehicle engine compartments, provides improved abrasion resistance, resistance to thermal oxidation and flame resistance.
In accordance with the present invention an insulated electrical conducting assembly is provided. The assembly includes an electrical conduit and an electrical insulating annular laminate which comprises an inner layer of a first polymeric composition and an outer layer of a second polymeric composition. The polymeric compositions are characterized by the requirements that (1) the hardness of the second polymeric composition is greater than the hardness of the first polymeric composition; (2) the abrasion resistance of the laminate is greater than the sum of the individual abrasion resistances of both the inner layer and the outer layer; (3) at least one of the first and second polymeric compositions is flame retardant; and (4) at least one of the first and second polymeric compositions is stabilized against thermal oxidation.